My 96 ram failed California smog test. Failed with a high NOX output, all other readouts were normal. The truck has over 200k miles with a 2.5yr hi-flow cat. I am thinking that it might be EGR valve, but I don't see it on the emission decal. I can't seem to find it on the 5.9 engine, is it bolted directly to the cylinder head? Any photos would help.

 

1996s Don't have EGR valves. Neither of mine do.

 

It's usually a lean condition and there could be a number of reasons for it. Maybe a vacuum leak, bad O2 sensor, exhaust leak before the cat, EGR... anything that would make it run lean could cause high NOx. Unless I'm wrong.

 

no help, but an interesting graph.
according to them - high nox = lean.

http://www.3si.org/forum/f36/failed-...50/index3.html

 

There a 3 things I can think of that will help a lean condition/emission issues. I'll list them from cheapest to most expensive:

1. Try running a 1/4th tank of gas with a 20 gallon bottle of chevron techron concentrate plus, and run 2 treatments of seafoam or Mopar Combustion Chamber Cleaner. That'll clean your injectors and combustion chamber of excessive carbon and it'll burn cleaner.

2. Try to relocate the IAT sensor to a cooler location, or run a 180* T-stat, both should throw a bit more fuel into the mix, but keep you in emissions standards. This is honestly cheaper than suggestion 1, but requires a bit of wrench knowledge.

3. After all that, replace the forward O2 sensors. One of them could easily be reading false and causing a lean out condition. I believe the Cali emissions trucks have 3 forward O2 sensors, not sure if 1 or all 3 effect fuel trims. The sensors aren't very cheap, but you could probably replace all 3 for about the cost of a shop diagnosis and 1 sensor.

 

Thanks everyone for the sugestions. I only have has 2 O2 sensors. I did notice that the radiator does need to be flushed, this could be another problem.